TELKOMNIKA ISSN: 1693-6930
Flicker Measurement and Grey Disaster Prediction of Grid-Connected .... Zhanqiang Zhang 393
in IEC61000-4-15,we should adopt the appropriate short-circuit ratio
n fic
k,
S S
. IEC 61400-21 standard recommends the short-circuit ratio is between 20-50.
For each network impedance phase angle
k
ψ
,the weighting procedure calculates the weighted accumulated distribution functions of the flicker coefficient
x c
P
r
,assuming four different wind distributions.For each accumulated distribution,the 99 percentile
,v c
ψ
a k
is reportedblock 4 and block 5 in Figure 1.
2.2. Flicker Assessment Procedures
If you get a flicker coefficient
,v c
ψ
a k
, you can calculate flicker
st
P
or
lt
P
on any specified site through the parameters of
k
S
,
k
ψ
and
a
v .The flicker emission from a single WTs during continuous operation shall be estimated applying the equation 2 below.
n st
lt k
a k
S P = P = c
ψ ,v S
2 In case more WTs are connected to the PCC, the flicker emission from the sum of them
can be estimated from the equation 3 below.
wt
N 2
st Σ
lt Σ
i k
a n,i
i=1 k
1 P
= P = c
ψ ,v S S
3 If the wind farm uses the same model of WTs, the flicker emission from the sum of them
can be simplified as the equation 4 below.
n,i st
Σ lt
Σ k
a WT
k
S P
= P = c
ψ ,v N S
4 Where
wt
N
is the number of WTs connected to the PCC.
3. Flicker Test 3.1. System Description
In this paper, the test data were measured on the BAIYUN wind farm in Inner Mongolia.The wind farm center is located about 109°5640 east longitude , 41°4446 north
latitude , with the average altitude of 1565m.The annual wind speed of this site at hub height is estimated to be 8 ms.The average wind power density is 523.6Wm
2
.The total installed capacity of the wind farm is 49MW, the rated power for a single WTs is 810KW, the output voltage is
0.69KV.The wind farm installed the double armature hybrid excitation WTs,which combine the advantage of VSCFVariable Speed Constant Frequency generator and CSCFConstant Speed
Constant Frequency generator.The generator has high power generation efficiency and simple control features.On the wind farm a step-up transformer substation with 220KV was
constructed. The main wiring diagram of the wind farm is shown in Figure 2.
ISSN: 1693-6930
TELKOMNIKA Vol. 13, No. 2, June 2015 : 391 – 400
394
Figure 2. Main wiring diagram of the wind farm Power quality measurements were taken from a single WTs terminal on the low voltage
side of the transformer TR1, which was shown at point A in Figure 2.We could calculate the flicker of multiple WTs connected to PCC by the equation 4.The measurement was carried out
from 16:10 on November 26,2013 to 12:00 November 26,2013,which had 1200 minutes in total. 3.2. Flicker Test
The measurement data of 10 min time series of instantaneous voltage and current were collected.The voltage and current sample frequency was 10.24 KHz, the wind speed sample
frequency was 5Hz and accuracy of the anemometer was ±0.2ms. In accordance with IEC 61400-21 standard, the measurement data of three-phase voltage and current were used to
calculate the flicker coefficient.The system was in equilibrium by analyzing the test data, so the data of phase 1 were used only.
3.2.1. Active and Reactive Power Test
The active and reactive power of the WTs were tested under the continuous operation state.The trend of the active and reactive power had consistency,which could be seen from
Figure 3.There was a certain proportional relationship between the active power and reactive power,
QP tan
, where φ was the power factor angle. Within the range of rated wind speed,
the output power of WTs increased with increasing wind speed.
TELKOMNIKA ISSN: 1693-6930
Flicker Measurement and Grey Disaster Prediction of Grid-Connected .... Zhanqiang Zhang 395
Figure 3. Active Power and Reactive Power
3.2.2. Relationship between Wind Speed and Flicker Coefficient
It can be seen from Figure 4 that the function relation between flicker coefficient and wind speed when the network impedance phase angle
k
ψ
are 30°,50°,70°and85°, the short- circuit ratio is 50.The larger grid impedance phase angle is, the greater flicker coefficient is .
Figure 4. Relationship between Wind Speed and Flicker Coefficient
3.2.3. Measurement of Short-term Flicker
The flicker of WTs can be measured from two aspects of continuous operation and switching operation. In this paper we studied the measurement of flicker under continuous
operation.The generation of flicker under continuous operation was caused by changes in wind speed, which caused the changes of reactive and active power.The measurement period of
short-time flicker is 10 minutes,the measurement period of long-time flicker is 2 hours.In the
ISSN: 1693-6930
TELKOMNIKA Vol. 13, No. 2, June 2015 : 391 – 400
396 continuous operation state,
st
P
and
lt
P
have the same flicker value. If the flicker value of WTs exceeds the limit value
st
P
=1, it would affect the operation of the power system. The upper limit values of
st
P
=1 and
st
P
=0.5 were marked in Figure 5.
st
P
=0.5 was the upper disaster limit value of flicker grey disaster prediction.
Figure 5. Measurements of Short-term Flicker
4. Model of Flicker Grey Disaster Prediction
